How to set login users as custom variable?

Support & Bugs
1

Hi, I am trying to set avariable that’s contains the users login
the issue is the the login user value is always overrides the old value.
I want to create asegment that make statictices for each login user in each login click.

2

the issue is the the login user value is always overrides the old value.

This is how Custom Variables work: http://piwik.org/docs/custom-variables/
But when the user does a new visit, then the value will not over-ride the value of the previous visit. It only overrides value for the current visit.